318 MISS DONALD ON PROTEROZOIC GASTEROPODA _[{ May 1902, 
Murchisoniide, and it would be convenient, at any rate provi- 
sionally, to regard them as a separate section or subgenus, for which 
I would suggest the name Cyrtostropha. At the same time, it is 
possible that further research may prove that these species are not 
all closely related one to the other, and further subdivision may be 
necessary. 
Another new species which I am describing is from the Wenlock 
Formation of Dudley, and is more like the type of Murchisonia than 
any other Silurian or Ordovician species with which I am acquainted 
in its robust form, the direction of the lines of growth, and the struc- 
ture and position of the band. The latter is not seen to be grooved 
as in WM. turbinata, Schloth., but this may possibly be the result of the 
manner of preservation, since it only occurs as an external mould. 
No evidence, however, is given of a slit in the outer lip, so it cannot 
be referred to Murchisonia without a query. 
From the material at present available, we find that, in the British 
Isles as well as in America, the elongated forms with a sinus or a 
notch precede those with a slit, and they also seem to do so in the 
Baltic Provinces. In the latter region the only shell recorded by 
Koken which may be a true Murchisonia is M. Meyendorfi, Kok. 
from Borkholm (Ordovician), but it is not clearly shown whether it 
possesses a slit. There are at least two, and possibly three, distinct 
groups of these sinuated shells with a band—the one containing 
Hormotoma, Ectomaria, etc., with the lines of growth sweeping back 
to and forward from the band very obliquely ; a second, containing 
Lophospira, having the lines of growth less oblique, and agreeing 
more in direction with those of Mwrchisonia, only the band is 
prominent instead of being grooved; Cyrtostropha may perhaps 
form a third group, having the lines of growth but slightly oblique 
and the band grooved. In a former paper’ I entered fully into 
the range of the genera Hormotoma and Ectomaria ; but, for the sake 
of comparison, I will here repeat it briefly. In the British Isles 
they apparently commenced in the Durness Limestone (Upper Cam- 
brian ?), and do not appear, so far as I know, after the close of 
the Silurian Period; indeed, Ectomaria is not represented later 
than the Ordovician. In America, Ulrich & Scofield state that 
Hormotoma commences in the Calciferous Group and extends to the 
end of the Silurian. They consider that Hormotoma is represented 
in the Devonian by M. desiderata and M. Maia, Hall: species 
which agree with Hormotoma in possessing strongly retreating and 
advancing lines of growth; but they say that a slit is added to the 
bottom of the sinus. Hctomaria appears to be confined to the 
Ordovician, both in America and in the Baltic Provinces. Hormo- 
toma ranges from the Ordovician and throughout the Silurian in 
the Baltic Provinces and Scandinavia. Lophospira, Whitfield, as 
emended by Ulrich, contains both elongated and short forms, and 
is said to range from the Calciferous Group upward to the middle 
1 Quart. Journ. Geol. Soe. vol. lv (1899) p. 251. 
ae 
